Secondhand smoke may increase a woman’s risk of miscarriage, stillbirth, and other pregnancy complications, finds a recent study in Tobacco Control.

Researchers at the Roswell Park Cancer Institute tracked data on more than 80,000 postmenopausal women who had taken part in the Women’s Health Initiative Observational Study. They found that women with the highest levels of secondhand smoke exposure—despite never having smoked themselves—had significantly greater risks for miscarriage, stillbirth, and tubal ectopic pregnancy.

The study’s authors noted that the longer the nonsmoking women were exposed to secondhand smoke, the greater their risk.

This study is significant because it considered lifetime secondhand smoke exposure, rather than only during pregnancy and reproductive years, and the comparison group of women who had never smoked was limited to women without any secondhand smoke exposure, producing a truer control group compared to previous studies, says Andrew Hyland, lead investigator.